A sentence fragment is a phrase wearing the clothing of a sentence.
It comes with the correct capital letter at the start, and a full stop at the end.
But it is not a sentence. Why? Because it does not have a subject (a noun or pronoun) and an active verb.
That fragment makes sense, but lacks the formal attributes of a sentence: a subject (noun or pronoun) and an active verb. It does not matter that it looks like a sentence on first glance.
That full stop is fancy dress, because the full stop and the comma are just the clothing we use to between distinguish a sentence (complete with subject and active verb) and a clause that has no right to be a sentence on its own.
Like many of the ‘rules’ of writing, using complete sentences is something that writers have to learn before they can decide to break the rules.
1. This [subject=pronoun] is [active verb] a sentence.
2. And this [subject=pronoun], a fragment.
Although the fragment in 2 makes sense when read directly after sentence 1, techniques like this require confidence in using ‘correct’ sentences.
So how could I transform 2 into a sentence?
By adding an active verb.
This is a fragment.
You may have noticed that I have also deprived the sentence of the ‘and’.
Well, this is because the fact that the phrase begins with ‘and’ is another clue that it might be a fragment. Accidental fragmentarians often make the mistake of putting a full stop into a place where a comma would be more grammatically orthodox. This imposter full stop is often inserted before the words ‘while’, ‘although’, ‘when’, ‘and’, ‘as’, and ‘but’.
While making this mistake.
See the problem? That last phrase follows on nicely from my previous sentence, but where is the subject, where is the verb?
I am not saying that you can never start a sentence with those words! But you need to look at the sentence that follows the word and identify a subject and active verb.
The wrong way looks like this:
Soldiers claimed their experiences changed them. While admitting their memories might deceive them.
Why is the second phrase a fragment? There are 2 reasons: first, there is no subject. The soldiers are marooned in the last sentence, and if you want them to sally forth into your next one, you need (at the very least) their pronoun: ‘they’. Second, there is no active verb. ‘Reflecting’ is a present participle. A present participle alone cannot a sentence make.
Historian [subject] reflecting on writing.
This would be fine as a title (titles can be fragments!) but it does not fulfil the job of a sentence.
Historian [subject] reflects [active verb] on writing.
Much better. (Oops.)
The simplest fix in these cases of fragmentation is to replace the full stop with a comma:
Soldiers claimed their experiences changed them, while admitting their memories might deceive them.
What if I want to keep the full stop? The following sentence would be equally correct:
Soldiers claimed their experiences changed them. However they [subject=pronoun] also admitted [active verb] that their memories might deceive them.
There may be those among you who wonder, who is this man and what has he done with the very same Will Pooley who told us to break all of the rules of grammar, to write differently?
The problem with fragments is that they obscure meaning. As I have already suggested, they are best used when the writer has reached a level of confidence in writing ‘correct’ sentences.
They are also closely related to another common writing problem: the run-on sentence.
Where the fragment is a phrase clothed as a sentence, but without its structure, a run-on sentence is really two or more sentences wearing the same outfit.
You cannot simply add whole sentences to one another using commas, the effect is incredibly draining on the reader, I am begging you please stop.
But perhaps that’s a discussion for another time.
In the meantime, why not brush up on your knowledge of fragments with these handy online quizzes from Purdue University: